The present invention relates to an elongated body made of reinforced plastic capable of resisting abrasion, and a process for its manufacture.
Such shaped bodies are usable, particularly but not exclusively, to manufacture highly resistant lightweight tubing by helical winding of the shapes. Tubes of this kind assembled in this fashion are described, for example, in U.S. Pat. No. 4,013,100.
It has already been proposed, for example, in French Patent 2,312,356 to make a shape of reinforced plastic by using a mixture of filaments and cross-linkable plastic to fill an elongated groove forming a mold, wound on the wall of a drum, with the shape being extracted from this groove after heat treatment.
During tests of bending fatigue of elements manufactured with shapes of this type, significant abrasion of the several layers thus formed has been observed, with the abrasion being capable of leading to premature failure of the tube.
French Patent 2,494,401 has already proposed a body of an elongated shape of reinforced plastic capable of resisting abrasion on at least three of its surfaces, and a process for manufacturing the elongated shaped body. However, the proposed shape is quite expensive, first because of the antiabrasion materials which it uses (quantity X unit price) and also because of the manufacturing cost. The latter increases as the width of the shapes decreases (dimension of the cross section of the shape along a perpendicular to the radius, with the height being the dimension along the radius) because the output of covering surface (composed of shapes) by the production machinery becomes smaller by the same proportion (covering surface output=rate of output of length multiplied by width of shape).
The present invention proposes a shape which is resistant to abrasion and a process for manufacturing the latter which overcomes the disadvantages of French Patent 2,494,401 cited above.
During fatigue testing of flexible tubing comprising several reinforcing sheets, it has been found that wear is irregularly distributed over the surfaces in question of the shape and that in all types of tubes and service configurations observed, the wear on the lower surfaces (internal surface of the shape) and upper surfaces (outer surface of the shape) is extremely severe and poses a serious danger to the tubing, while the wear on the side surfaces has no serious effects in the very long term.
The wear on the lower and upper surfaces corresponds to the contact zones where the effect of a high sliding speed is added to that of a high degree of friction, linked to a high contact force between the upper surfaces of the shaped bodies of a first sheet and the lower surfaces of the shaped bodies of a second sheet in contact with the first sheet at the surfaces.
To overcome this damage to the surfaces, a suitably selected antiabrasion material can be placed between them and also, for reasons of stability of the latter, it can easily be rendered integral with one or the other of the surfaces. Thus, by using only a single layer of antiabrasion material, the quantity of the antiabrasion material is reduced to a minimum and because of its high cost, the maximum reduction is achieved in the cost of abrasion-resistant shaped bodies.
According to an especially economical manufacturing process, the present invention proposes to create abrasion-resistant shapes by making the antiabrasion material integral with the upper surfaces of the shaped bodies and simultaneously producing several shapes.
The present invention, in addition to the economic advantages which it confers, makes it possible to facilitate the installation of shaped bodies when winding reinforced tubing and cables, particularly those which comprise a large number of shaped bodies per reinforcing sheet.
In addition to the same advantages as outlined above, the present invention also offers the possibility of manufacturing shaped bodies which comprise an antiabrasion material which is on both the lower surface and the upper surface.
By virtue of the process of the present invention it is possible, especially for tubing comprising three superimposed sheets of shapes, to limit the number of abrasion-resistant shapes. By using shapes to form the central sheet which are resistant to abrasion on both their lower and upper surfaces, it is sometimes useless to use abrasion-resistant shapes to produce the extreme sheets.
In accordance with the process for manufacturing according to the invention, an elongated body of reinforced material capable of resisting abrasion and comprising a lower and an upper surface is provided with the process utilizing an elongated groove forming a mold which is filled with the reinforced material, and before the groove is filled with the reinforced material, a first layer of antiabrasion material is placed on the bottom and/or walls of the groove and/or after having lined the groove with the reinforced material, it is covered with a second layer of antiabrasion material. After having carried out one and/or the other of the preceding steps, the groove is separated from the reinforced material comprising the layer or layers of antiabrasion material.
When the reinforced material is a mixture of stabilizable plastic and high-resistance filaments, the first layer of antiabrasion material can be applied before proceeding to the treatment that permits the shape of the stabilizable material to be stabilized.
To manufacture curved elongated bodies using a hollow shaped mold, the elongated bodies could be shaped in the hollow shape arranged in a helix on a mandrel, and after forming the elongated body comprising the layer or layers of antiabrasion material, they could be separated from the hollow shape.
The mold could comprise several essentially parallel grooves, making it possible to produce several abrasion-resistant bodies simultaneously.
The layer or layers of antiabrasion material could be in the form of a strip.
All the upper surfaces of the elongated bodies could be covered simultaneously to protect them against abrasion, using a single strip of antiabrasion material.
The strip could include a restriction zone between each elongated body.
After having separated the shape which forms the mold for the shaped elongated bodies covered by the antiabrasion strip, the strip could be divided longitudinally between the elongated bodies to produce simultaneously several shaped elongated abrasion-resistant bodies.
The shaped bodies could be separated from one another during the use of the reinforced body, with the reinforced body comprising the shaped bodies.
The invention also provides a shaped body obtained by working the process.
The invention also provides a curved elongated abrasion-resistant body, specifically characterized by the fact that the upper surface and/or the lower surface of the elongated body is/are resistant to abrasion and by the fact that one part at most of the lateral surfaces of the body is resistant to abrasion.
The internal walls of the mold could be lined with an antiadhesive product before adding the filaments of cross-linkable material.
The elongated body could comprise an antiabrasion material only on its upper surface and/or lower surface.
The invention also provides for a strip having at least one surface and grouping the parallel elongated bodies with the bodies having to be used simultaneously. This strip is characterized by each of the elongated bodies comprising a surface which is integral with a part of the surface of the strip and characterized by the fact that in the course of the utilization of the elongated bodies, with the strip being designed so that the elongated bodies acquire a relative freedom of movement between them.